I tend to think it may have made a major impact as far as increasing German losses. The 303 caliber is a relatively poor performer when judged as a rifle, being bettered by the 30.06 by quite a margine, when used against aircraft its shortcomings would be hugely magnified. I think had all Spitfires and Hurricanes been instead using 6 50's then German losses would have increased and British losses decreased. The British fighters could have stayed out of effective range of the German bombers defensive armament and still have a much more effective punch. How many German aircraft got home because the pathetic 303 stopped before it penatrated a fuel tank, control cable, engine block or pilot? The 50, on the other hand would have punctured the tank, severed the control cable, busted the engine block or killed the pilot. Any thoughts?

I tend to think it may have made a major impact as far as increasing German losses. The 303 caliber is a relatively poor performer when judged as a rifle, being bettered by the 30.06 by quite a margine, when used against aircraft its shortcomings would be hugely magnified. I think had all Spitfires and Hurricanes been instead using 6 50's then German losses would have increased and British losses decreased. The British fighters could have stayed out of effective range of the German bombers defensive armament and still have a much more effective punch. How many German aircraft got home because the pathetic 303 stopped before it penatrated a fuel tank, control cable, engine block or pilot? The 50, on the other hand would have punctured the tank, severed the control cable, busted the engine block or killed the pilot. Any thoughts?

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Your theory neglects the adverse effects of the weapon on the platform itself. The .50 Browning weighed in at around 38Kgs while the .303 was around 13.4Kgs so even x3 .50s would weigh significantly more than the x4 .303s they would be replacing.

The weight of a .50 calibre round is 40g whilst the weight of a .303 round is 11.4g, now stretch that weight differential out along an ammunition belt.

These weight penalties WOULD make a difference, especially in fighters that were prevalent at the beginning of the war; the Spitfire would have developed wing blisters much earlier in its career and the Hurricane would have been even slower. It wasn't until much later in the Spitfire's development career that the 'e' wing (as deployed on the Mk IXe) would be able to house a similarly weighty armament.

There would also be less ammunition available, as larger calibre rounds will take up the same space, more quickly. With this in mind, hitting power is one thing, hitting the target is quite another and most of the young guys in the BoB were, by their own admission, hardly marksmen; if you're squirting the target looking for a bead using .50 calibre weapons, you would find you've run out of squirts alot faster than you would have done with your old .303s.

The previous post by adler was pretty much on the money. If anything, the use of the .50 in the configuration you have suggested, on machines that were in all honesty not technically ready for them, could even have been to the detriment of the RAF at the BoB stage.

Interesting theory. But as far as the Spit goes, the Mk IIa had 8 303's while the Mk IIb had 2 20mm and 4 303's, so I don't think 6 50's would have decreased performance of that aircraft. The Hurricanes job was intercept bombers(supposedly) while the Spits engaged the fighters so a slight decrease in top speed shouldn't have bothered it either, if in fact it did slow it down. As far as gunnery goes, have you ever seen pictures of German bombers they did shoot down? They look like a kids bb gun target with hardly a square inch that doesn't have a bullet hole in it. The Hurricane only carried 333 rounds per gun, so my guess is that in order to bring down a twin engine bomber with 303 caliber weapons, they had to get in close and dump most of their ammo on one target. I have certainly never read about British pilots getting the multiple kills on one mission that American pilots were able to score against the Japanese. I believe that is because after shooting down 1 He111 or Do17 they were out of ammo or low enough they couldn't scratch down another one with what they had left.

The US fighters went away from the 30 cal MG very fast once the war began. The 3006 was somewhat more powerful than the 303 British but it was found inadequate against enemy AC. Your point is well made though about gunnery. A lot of the BOB RAF pilots barely could fly their fighter much less have any gunnery skills. The point about weight and the small size of the British fighters is important also. The F4F3 weighed roughly 1000 pounds more than the Spit and had a thicker wing so 4-50s and 400 rounds per gun worked well for it especially as it's pilots were very well trained in gunnery, especially deflection shooting. The Hurricane probably would have been a better candidate for the armament load of the Wildcat except for gunnery skills of the pilot.

1. ..as far as the Spit goes, the Mk IIa had 8 303's while the Mk IIb had 2 20mm and 4 303's, so I don't think 6 50's would have decreased performance of that aircraft.

2. The Hurricanes job was intercept bombers(supposedly) while the Spits engaged the fighters so a slight decrease in top speed shouldn't have bothered it either, if in fact it did slow it down.

3. I have certainly never read about British pilots getting the multiple kills on one mission that American pilots were able to score against the Japanese.

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1. I've no idea what the Hispano 20mm cannon weighed but I can imagine it was heavier than the .50 by some margin. It would be limited to something like 120 to 150 rounds per gun though.
Of note, it's interesting that you are looking at the potentially positive effects that a heavier calibre weapon would have had on the BoB and when countered with the added weight theory, go on to propose a similarly weighty weapon, the Hispano.
This was fielded by one squadron during the BoB (19 Sqn, Spitfire Ib) and they endured a torrid time, eventually requesting their .303-armed mounts back quite vigorously.
It's not enough to say it eventually became a winner, the fact is, during the BoB, it wasn't. Designed for the rigid environment of the engine bay, it just couldn't live with the flexure of the wing-mounted application, very often getting off just one shot before jamming ie no positive effect on the BoB kill tallies.

Technically, the platforms of the time (the BoB phase) just weren't ready for it although in fairness, this doesn't mean the .50 would have suffered in the same way.

2. Later in the war, when USAAF flight leaders started receiving their P51-Ds with the extra x2 .50s, they immediately started complaining that their flights (P51-Bs) were 3-5mph faster than they were; if it's going to do that to an advanced design like the Mustang, it's going to do that to an old kite like the Hurricane and the Hurricane couldn't afford it like the Mustang, it was already slow.

3. A rather ill-founded comparison, regardless of what effects the .50 would have had on BoB kill tallies, the fact is that the .303 is what they had and they were shooting at the aircraft of a nation whose design philosophy was to include armour protection.
Now fast-forward to the times when the USAAF are engaging the Japanese and you see the US design philosophy of heavy machine-guns engaging the Japanese design philosophy of agility over protection (ie no armour).

I don't think there is any doubt that 6 x .50 are far more effective than 8 x 303, so the obvious reply would be that the Germans would have lost more aircraft.
Personally I think the Hurricane had a better chance carrying the 6 x 0.50 as the weapons bay was a better size and they didn't seem to have a problem with 4 x 20. I do doubt that the Spitfre could carry 6, 4 x 0.50 sounds a better bet. That said 4 x 0.5 us probably better than 8 x 303 so a similar situation would apply.

I have read of German bombers getting home with 200 hits from the 303, only just maybe, but still getting home. If you were using 6 x 0.50 that would equal approx 95 hits by 0.50 and I have not heard of a medium bomber taking that much damage.

I may be wrong but I thought that the 20 mm cannon of the Spitfire, at least the early version, only carried a 60 round magazine? I read they had jamming problems with them also. I didn't know that ANY RAF aircraft had 20 mm during the BoB, interesting. Agreed on Japanese airplanes being 1 shot lighters, while German planes were much better with armor and self sealing tanks. Neither compared well against American medium bombers for defensive fire and taking battle damage. Its probably a good thing that the Germans didn't have the B25 or B26.

You are correct when you say that the early British 20mm only had 60rpg, however the same limitation applied to early German, French, American and Japanese 20mm installations.
The RAF had one squadron of Spitfires with the 20mm (note they only had the 2 x 20mm, no additional LMGs as in later versions) and certainly one maybe two Hurricanes. The Spitfires had terrible jamming problems and were replaced by standard Spitfires, to a large part due to the guns being mounted on their side, The Hurricane carried the guns in a fairing below the wing and this had a significant impact on the performance of the aircraft, but it worked and at least one German bomber was shot down at a distance that would have been almost impossible with the 303.

Pinsog, Glider
you're both right, the 20mm was indeed limited to 60rpg, I don't have a great deal on the Hispano and took a guess.

I stick with my main argument that while on paper the heavier calibre weapons certainly looked more appealing, I don't believe that the airframe/powerplant development of the time was sufficient to exploit it, at least, not fully enough to have made a significant impact on the BoB.
Both F.36/34 (Hurricane) and F.37/34 (Spitfire) were designed with the .303 in mind with no thought at the time for heavier-calibre weapons, which would have necessitated a strengthened wing.

With the Spitfire, this was proved in the case of the Hispano. It didn't like lying on its side and wasn't designed with the flexing environment of the wing in mind. Having a significantly larger breech than the .303, the .50 may well have needed to be canted in a similar fashion to the early P51 installations and we know what happened there.

The Hurricane was a significantly better gun platform but the added weight of the .50 installations would have robbed it of even more performance.

The majority of Battle of Britain Hurricanes Spitfires were powered by the 1,030 hp Merlin engine. Hence, IMO it is not relevant to compare armament of later versions e.g. the Hurricane Mk IIC with four 20 mm canon didn't see service till May '41 and were fitted with a more powerful engine.
Moreover, as been already mentioned by others the weight of the 0.50" and 0.303" precludes six instead of eight practical.
Hence, the alternative to consider would be four 0.50" rather than Eight 0.303". Of interest here is the order by the Belgiums for Hurricances - licensed produced aircraft would be armed by 12.65 mm Browning guns.
Effectiveness in the 'battle' should have been better - with the longer range of the 0.50" weapon, also the eight 0.303" suffered byh the shotgun effect - the spread covered a wide area.
What saved though the 0.303" weapon was the Dixon incedinary bullet (too often refered to by the cover name of de Wilde).

There would be no problem mounting 4 x.50s in a Spitfire wing, they would fit easily (right side up) in the same positions as the .50 and Hispano in an E wing (with E type modifications so ammo bays fit etc).

This would give approximately 55kg of .50 ammo (325 rds per gun), compared to 24 kg for the 8 x .303s. 120 kg for the .50 guns compared to 80 kg for the .303 guns. Total weight increase approximately 64 kgs (140 lbs).

Testing the Spit I (1939 with 2 speed prop) with 2x20 Hispanos compared to 8x.303s showed a decrease of only 3mph max speed at alt with climb rate virtually unaffected.

If you only mounted 4 50's instead of 6, wouldn't that leave more room for ammo?
I also found a book that talked about the Spits that had 20's during the BoB. One pilot said that 60 round magazines only gave them 6 seconds of firing time and they never got to fire all 60 rounds due to jamming so they traded them in for some all 303 armed aircraft.
Anyone got any idea of the effective range of 8 303's in air to air combat?

The max effective practical range of the US 30 cal which was more powerful than the 303 was 200 yards and the energy at that range for the 303 would be about 1386 foot pounds. For a comparison, 1000 foot pounds of energy is considered minimum for killing a deer.

If you only mounted 4 50's instead of 6, wouldn't that leave more room for ammo?

I also found a book that talked about the Spits that had 20's during the BoB. One pilot said that 60 round magazines only gave them 6 seconds of firing time and they never got to fire all 60 rounds due to jamming so they traded them in for some all 303 armed aircraft.

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Possibly but what are you asking, if you fitted x6 .50 cals or fitted x4 .50 cals? I seem to remember your original what-if enquiring about 6.

I did mention the cannon-armed Spitfires deployed during the battle; they were an unqualified failure and even if they weren't, it's reasonable to assume that the (generally) less than impressive gunnery skills of the inexperienced British pilots would not have turned 6 seconds (roughly two decent bursts) of firing time to their advantage.

You were right about the cannon armed Spits, I was just agreeing with you, I found it last night in one of my books.
My original question was about 6, but if you feel they would have been to heavy(I don't think they would, especially for the Hurricane) what about 4 and a larger supply of ammo per gun. If they were having to get to point blank range to hit them anyway, I doubt that 4 50's with a decent ammo supply would have been any harder to hit with. One Spitfire pilot with 20mm said one of his 20's jammed throwing the aircraft sideways and he had to get so close to an Me110 to hit it that he nearly cut the tail off with his prop. If your gonna be that close I think even 4 50's would have been devistating. With a bigger supply of ammo and only 4 50's, they might have been able to down more than 1 target per aircraft.